Patent GB-744579-A (GB)
Title: Separation and purification of 2-methyl 5-vinylpyridine by distillation and crystallisation
Filed: 1953-12-31
Abstract: In the preparation of 2-methyl-5-vinyl pyridine by the catalytic dehydrogenation of 2-methyl-5-ethyl pyridine, the 2-methyl-5-vinyl pyridine is recovered from unchanged ethyl pyridine and side reaction products by distilling the mixture to separate the 2-methyl-5-ethyl pyridine and leave a residue containing 65-95 per cent vinyl pyridine which is crystallized under "static conditions," e.g. by heat exchange with a cooled surface without stirring and without transfer of crystals from the mother liquor; the crystal deposit is then subjected to gradual heating so that melted or sweated material drains away and washes the remaining crystals.  The products of the catalytic dehydrogenation of 2-methyl-5-ethyl pyridine in the presence of steam were separated into water and oily layers.  The oily layer was dehydrated under reduced pressure and flash distilled at 5 mm. pressure in the presence of N-phenyl-beta-naphthylamine as inhibitor.  The product containing 24 per cent by weight 2-methyl-5-vinyl pyridine was fractionated at 6-7 mm. pressure until the percentage in the residue was increased to 72.5 per cent.  This residue was flash distilled to remove polymers and inhibitor and then crystallized in an inverted Erlenmayer flask with a neck sealed into the bottom, the original neck being drawn out and sealed to a 6 mm. tube to form an outlet for draining mother liquor.  The flask was charged with the plug in position and cooled to -25 DEG  C.; then seeded with crystals and cooled to -40 DEG  C.; after 15 minutes suction was applied to drain off mother liquor and the current of air applied caused sweating of the crystals.  After removal of the mother liquor 2-methyl-5-vinyl pyridine of 96 per cent purity was recovered.ALSO:In the preparation of 2-methyl-5-vinyl pyridine by the catalytic dehydrogenation of 2-methyl-5-ethyl pyridine, the 2-methyl-5-vinyl pyridine is recovered from the unchanged ethyl pyridine and side reaction products by distilling the mixture to separate the 2-methyl-5-ethyl pyridine and leave a residue containing 65-95 per cent vinyl pyridine and crystallizing the 2-methyl-5-vinyl pyridine under "static conditions" e.g. by heat exchange with a cooled surface without stirring and without transfer of crystals from the mother liquor; the crystal deposit is subjected to gradual heating so that melted or sweated material drains away and washes the remaining crystals.  As exemplified the products of the catalytic dehydrogenation of 2-methyl-5-ethyl pyridine in the presence of steam were separated into water and oily layers.  The oils layer was dehydrated under reduced pressure and flash distilled at 5 mm. pressure in the presence of N-phenyl-beta-naphthylamine as inhibitor. The product containing 24 per cent by weight of 2-methyl-5-vinyl pyridine was fractionated at 6-7 mm. pressure until the percentage in the residue was increased to 72.5 per cent.  This residue was flash distilled to remove polymers and inhibitor and was then crystallized in an inverted Erlenmayer flask with a neck sealed into the bottom the original neck being drawn out and sealed to a 6 mm. tube to form an outlet for draining mother liquor.  The flask was charged and cooled to -25 DEG C; then seeded with crystals and cooled to -40 DEG C; after 15 mins. suction was applied to drain off mother liquor and the current of air applied caused sweating of the crystals.  After removal of the mother liquor 2-methyl-5-vinyl pyridine of 96 per cent purity was recovered.